System and method for solar energy capture and related method of manufacturing

ABSTRACT

A system and method of capturing solar energy, and related method of manufacturing, are disclosed. In at least one embodiment, the system includes a first lens array having a plurality of lenses, and a first waveguide component adjacent to the lens array, where the waveguide component receives light, and where the waveguide component includes an array of prism/mirrored facets arranged along at least one surface of the waveguide component. The system further includes at least one photovoltaic cell positioned so as to receive at least a portion of the light that is directed out of the waveguide. A least some of the light passing into the waveguide component is restricted from leaving the waveguide component upon being reflected by at least one of the prism/mirrored facets, hereby the at least some light restricted from leaving the waveguide component is directed by the waveguide toward the at least one photovoltaic cell.

CROSS-REFERENCE TO RELATED APPLICATIONS

This patent document is a continuation of U.S. patent application Ser.No. 13/119,955, having a filing date of Jun. 3, 2011, which is a 35U.S.C. §371 National Stage Application of International Application No.PCT/US2009/057567, filed on Sep. 18, 2009, which claims the benefit ofU.S. Provisional Patent Application No. 61/098,279 entitled “System andMethod for Solar Energy Capture and Related Method of Manufacturing” andfiled on Sep. 19, 2008, all of which are incorporated by referenceherein.

FIELD OF THE INVENTION

The present invention relates to solar energy systems and methods and,more particularly, to systems and methods for capturing solar energythat operate at least in part by way of concentrating received lightprior to conversion of the light into electrical or other power, as wellas to methods of manufacturing such systems.

BACKGROUND OF THE INVENTION

Solar energy systems are of greatly increased interest due to risingenergy demands worldwide and consequent rising prices for existingenergy resources, especially petroleum resources. While much effort isbeing focused upon developing more efficient photovoltaic (PV) cellsthat can generate ever greater amounts of electrical energy based upon agiven amount of solar radiation directed upon those cells, highefficiency PV cells nevertheless remain expensive. A less-expensivealternative to employing high efficiency PV cells is to employ low (orlower) efficiency PV cells. However, such PV cells need to beimplemented across larger surface areas in order to collect sufficientsolar radiation so as to generate the same amount of energy as candeveloped using high efficiency PV cells having a smaller surface area.

Although the efficiency of a PV-based solar energy system depends uponthe efficiency of the PV cell(s) employed in that system, the amount ofenergy generated by such a system can also be enhanced withoutincreasing the efficiency of the PV cell(s) or larger area PV cell(s) bycombining the use of PV cell(s) with additional devices that concentratethe solar radiation prior to directing it upon the PV cell(s). Becausesuch solar concentration devices can employ components that are lessexpensive than the PV cell(s) themselves, a solar energy systememploying such a solar concentration device in combination with PVcell(s) covering a relatively small surface area can potentiallyproduce, at a lower cost, the same high level of energy output as thatachieved by a solar energy system employing only PV cell(s) of the sameor greater area. Also, a solar energy system employing such a solarconcentration device in addition to high efficiency PV cell(s) coveringa relatively small area can achieve higher levels of energy output thanwould be possible using those PV cell(s) alone, even if those cellscovered a large area.

While potentially providing such advantages, existing solar energysystems employing both PV cell(s) and solar concentration devices havecertain disadvantages as well. In particular, some stationary solarconcentration devices tend to be not very efficient. For example, oneparticular type of existing solar energy system employing both PVcell(s) and solar concentration devices is a system employing one ormore fluorescent solar concentrators (FSCs). In such a device, lightincident on the surface of a slab waveguide is absorbed by an atomic ormolecular transition of material embedded in the slab. Upon absorption,some of the energy is then emitted as fluorescence uniformly in alldirections, and this fluorescent light is emitted at a longer wavelengthwith less energy than the incident light. While a fraction of theemitted fluorescence is trapped within the slab, and guided to an edgeof the waveguide for illumination of a PV cell, a large fraction of thefluorescent light is re-absorbed and re-emitted into a non-guideddirection, thus resulting in substantial inefficiency.

An additional problem associated with some conventional solarconcentrators (e.g., imaging lens or mirror-based concentrators) isthat, for proper operation, such solar concentrators require sunlightthat is incident from a particular direction relative to theconcentrator. That is, while such solar concentrators are able tocondense/magnify light incident over a large area onto a smaller area PVcell, such large magnifications require precise alignment that must bemaintained as the sun moves through the sky through the daily arc, andthrough the seasonal variation of elevation. Although it is possible toachieve such alignment by way of an “active” system that uses tracking(with or without positional feedback), such active systems are expensiveand often complicated to implement. The alternative, “passive” systems,which do not use active alignment, can achieve only a relatively smallconcentration factor (e.g., of approximately 10 suns), depending on therange of angles over which the concentrator is designed to maintainrelatively high throughput efficiency.

Still another disadvantage associated with at least some conventionalsolar energy systems employing solar concentrators is that they arecomplicated and/or expensive to manufacture.

It would therefore be advantageous if an improved design for a solarenergy system employing both PV cell(s) and solar concentration devicescould be developed. More particularly, it would be advantageous if suchan improved design allowed for one to achieve one or more of thebenefits of conventional solar energy systems employing both PV cell(s)and solar concentration devices, while not suffering from (or sufferingas much from) one or more of the above-described disadvantages of suchsystems.

SUMMARY OF THE INVENTION

The present inventors have recognized the desirability solar energysystems employing PV cells in addition to solar concentrators, andfurther recognized that existing systems employing fluorescent solarconcentrators (FSCs) are advantageous in that, insofar as they employslab waveguides, such systems can be more compact than many other formsof solar energy systems that employ other forms of solar concentrators.Additionally, however, the inventors have further recognized that a newform of solar energy system employing slab waveguides can be achievedhaving higher efficiency than existing systems if, instead of employingFSCs, the solar concentrators instead are built by placing a lens arrayadjacent to a slab waveguide formed between a low index cladding layerand an additional layer having prism facets, with the lens array beingalong the cladding layer opposite the additional layer of the slabwaveguide having the prism facets. By appropriate design of the prismfacets, total internal reflection can be achieved within the slabwaveguide with respect to much if not all incoming light directed intothe slab waveguide, and this light can in turn be directed to one ormore PV cells positioned at one more ends/edges of the slab waveguide.

Additionally, the present inventors have also recognized thedesirability of solar energy systems that are capable of receiving lightfrom changing angles of incidence. Consequently, while prism facets withconstant optical properties can be employed in at least some embodimentsof the present invention, the present inventors have further recognizedthat in at least some other embodiments of the present invention theprism facets can be formed or revealed by way of one or more materialsand/or processes that allow for the prism facet characteristics to vary,including location relative to the microlens, depending upon the lightincident upon those prism facets. Also, in at least some otherembodiments, components of the solar energy systems can be shiftedslightly in various manners to also allow light of various angles ofincidence to be received and directed to PV cells. In some suchembodiments, the waveguide with the prism facets can be shifted relativeto one or more lens devices. Further, the present inventors have alsorecognized the desirability of increasing the degree to which light isconcentrated onto less numbers of (or smaller) PV cells, as well as thedesirability of being able to receive multiple light components ratherthan merely a single light component or single range of lightcomponents, and have further developed various arrangements thatfacilitate achieving such objectives.

In at least one embodiment, the present invention relates to a systemfor capturing solar energy. The system includes a first lens arrayhaving a plurality of lenses, and a first waveguide component adjacentto the lens array, where the waveguide component receives light, andwhere the waveguide component includes an array of prism or mirroredfacets (or other light-directing feature) arranged along at least onesurface of the waveguide component. The system further includes at leastone photovoltaic cell positioned so as to receive at least a portion ofthe light that is directed out of the waveguide. At least some of thelight passing into the waveguide component is restricted from leavingthe waveguide component upon being reflected by at least one of theprism or mirrored facets, whereby the at least some light restrictedfrom leaving the waveguide component is directed by the waveguide towardthe at least one photovoltaic cell.

Further, in at least one embodiment, the present invention relates to amethod of manufacturing a solar energy collection system. The methodincludes providing a waveguide layer, providing a lens array incombination with the waveguide layer, and forming prism or mirroredfacets on the waveguide layer by exposing the waveguide layer and atleast one additional layer to light.

Additionally, in at least one embodiment, the present invention relatesto a method of capturing solar energy. The method includes receivinglight at a waveguide component, and reflecting at least a portion of thereceived light at a plurality of prism or mirrored facets formed along asurface of the waveguide component, where substantially all of thereflected light experiences total internal reflection within thewaveguide component subsequent to being reflected by the prism ormirrored facets. The method also includes communicating the reflectedlight within the waveguide component toward an edge surface of thewaveguide layer, and receiving the communicated reflected light at aphotovoltaic cell upon the communicated reflected light beingtransmitted through the edge surface.

Further, in at least one embodiment, the present invention relates to asystem for capturing solar energy. The system includes an opticalwaveguide layer, having an upper and lower cladding layer, and a lensarray having a plurality of lenses, disposed above the upper claddinglayer, and upon which sunlight is incident. The system also includes anarray of injection features formed on the optical waveguide layer andarranged so that each injection feature is located at or near the focusof a respective one of the lenses, wherein each of the injectionfeatures is oriented so that light focused from the lens onto therespective injection feature is coupled into the optical waveguidelayer. The system further includes at least one photovoltaic cellpositioned along at least one edge surface of the optical waveguide,wherein the light coupled into the optical waveguide layer is guided bythe waveguide toward and absorbed by the at least one photovoltaic cell.

In at least one further embodiment, the present invention relates to asolar photovoltaic system that includes a solar concentrator thatcollects direct sunlight into a small-area PV cell, overlapping in lightcollection area with a non-concentrated solar panel that collectsindirect sunlight into a large-area PV or solar-thermal panel.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic, perspective, exploded view of an additionalexemplary solar energy device employing components allowing forconcentration and collection of incoming light, in accordance with atleast one embodiment of the present invention;

FIG. 2 is a schematic, cross-sectional elevation view of the solarenergy device of FIG. 1 that particularly illustrates exemplary lightpaths that occur within that device;

FIG. 3 is a schematic diagram illustrating exemplary steps of amanufacturing process that can be employed to produce a device such asthat shown in FIGS. 1-2;

FIGS. 4A-4C are flow diagrams further illustrating other exemplarymanufacturing processes that can be employed in producing a device suchas that shown in FIGS. 1-2;

FIG. 5 is an additional schematic, cross-sectional elevation view of thesolar energy device of FIG. 1 illustrating possible exemplary operationwhen incident light impinging the solar energy device is tilted relativeto an axis normal to the solar energy device;

FIG. 6 is a schematic, cross-sectional elevation view of a furtherexemplary solar energy device differing from that of FIGS. 1-2,particularly in that it employs materials that react to sunlight toefficiently couple light which is incident from a range of angles into awaveguide layer, in accordance with another embodiment of the presentinvention;

FIG. 7 is a flow chart illustrating exemplary steps of operation of thesolar energy device of FIG. 6, particularly in terms of its reaction topositional variation of sunlight;

FIGS. 8-14 are additional schematic, cross-sectional elevation views ofadditional exemplary embodiments of solar energy devices that employvarious forms of micro-tracking;

FIGS. 15-17 are additional schematic, cross-sectional elevation views offurther exemplary embodiments of solar energy devices that allow fordiffer manners of extraction of light from waveguides of the solarenergy devices;

FIG. 18 is an additional schematic, perspective view of a solar energysystem in the form of a planar concentrator array;

FIGS. 19-23 are additional schematic, cross-sectional elevation views offurther exemplary embodiments of solar energy devices that allow forvarious spectral components of light to be directed to different PVcells;

FIGS. 24A-24D, 26A-C and 28B are further schematic perspective views ofportions of additional exemplary embodiments of solar energy devicesthat are arranged to facilitate various manners of concentration oflight; and

FIGS. 25, 27 and 28A are additional schematic views illustrating mannersof concentration employed by some of the solar energy devices shown inFIGS. 24A-24D, 26A-C and 28B as well as at least one other type of solarenergy device.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to FIG. 1, an exploded view of a solar energy system 2 inaccordance with one embodiment of the present invention is provided. Asshown, the solar energy system 2 includes a solar concentration section4 and multiple PV cells 6. The solar concentration section 4 can also bereferred to as a micro-optic concentration section in view of the smallsize of the structure and its components relative to the overallphysical structure of the system 2. More particularly as shown, thesolar concentration section 4 includes a lens array 8 having multiplelenses 10 arranged substantially along a plane. The lenses 10, which inthe present embodiment are formed by embossing the lenses on a surfaceof glass or plastic superstrate, can be referred to as microlenses,again in view of their size relative to the overall physical structureof the system 2. Sunlight (or possibly other incoming light) is incidentupon an outer surface 12 of the lens array 8, and exits the lens arrayby way of an inner surface 14 on the opposite side of the lens arrayrelative to the outer surface.

In addition, the solar concentration section 4 further includesadditional waveguide portions 19 (aside from the lens array 8). Theadditional waveguide portions 19 include a low index cladding layer 16and a slab waveguide 18. When the solar energy system 2 is assembled,the low index cladding layer 16 is positioned in between the lens array8 and the slab waveguide 18. The low index cladding layer 16 can be, forexample, a Teflon AF or related fluoropolymer material, while the slabwaveguide 18 can be made from glass (e.g., F2 flint glass) or an acrylicpolymer. The slab waveguide 18 has a thickness 20, an inner surface 22that is in contact with the low index cladding layer 16 (when thesection 4 is assembled) and an outer surface 24 opposite the innersurface and separated from the inner surface by the thickness 20. Aplurality of prism facets 26 are formed along the outer surface 24. Therespective prism facets 26 are aligned with the respective lenses 10 andthe thickness 20 is determined so that a respective focal point of eachof the lenses occurs at a respective one of the prism facets. Asdiscussed below, in practice, the prism facets 26 are much smaller inextent relative to the lenses (for descriptive purposes, the prismfacets are not drawn to scale in FIG. 1).

The prism facets 26 are intended to be representative of a variety ofdifferent types of injection facets or injection features that areconfigured to refract, reflect, diffract, scatter, and/or otherwisedirect light incident thereon so that the light entirely orsubstantially remains within the slab waveguide 18 or at least is partlyrestricted from exiting the waveguide, any and all of which areencompassed by the present invention. While the prism facets 26particularly can be considered as injection features that are largely orentirely refractive in their operation, other forms of injectionfeatures also encompassed by the present invention such as mirroredfacets can be considered largely or entirely reflective. In someembodiments, the injection features employed will provide any one ormore of refraction, reflection, diffraction (e.g., in the form of adiffraction grating) or scattering. As discussed further below, theprism facets 26 (or other light directing/injection features) can beformed using any of a variety of techniques that can involve, forexample, embossing, molding, ruling, lithography, or photolithography.In some embodiments, the outer surface 24 of the waveguide 18 includesan additional cladding layer in addition to the prism facets 26.

The overall optical collection efficiency of the concentrator/solarenergy system depends upon, among other things, the exact lateral andvertical position of the injection features (e.g., the positions of theinjection features relative to lenses), as well as on the physicalprofile of the injection features (the shapes and orientations of one ormore particular facet surfaces of the injection features). Among otherthings, the angle(s) of the injection features (e.g., the angles ofsurfaces of the injection features relative to the outer surface 24 ofthe waveguide 18 on which those injection features are mounted) can beof significance. Often these angles are determined in a manner thattakes into account the angle(s) at which light is expected to impingethe injection features. For example, where light is expected to impactone of the prism facets 26 at smaller angles (e.g., 0 to 15 degreesrelative to an axis normal to the outer surface 24 of the waveguide 18),the angle of the facet surface relative to the outer surface 24 can be30 degrees, while where light is expected to impact one of the prismfacets at larger angles, the angle of the facet surface relative to theouter surface 24 can be 45 degrees. It will be understood that, indeveloping any given solar concentrator, one can employ optical designsoftware to generate injection feature profiles that are appropriategiven the combination of material properties and physical andfabrication constraints (and expected operational constraints) thatapply to that particular embodiment.

Further as shown, the inner and outer surfaces 22, 24 of the slabwaveguide 18 are each rectangular, such that the slab waveguide 18 hasfirst, second, third and fourth edge surfaces 28, 30, 32 and 34,respectively, extending between the inner and outer surfaces, where thefirst and second edge surfaces oppose one another and the third andfourth edge surfaces oppose one another. While fully-reflecting coatingscan optionally be applied to the third and fourth edge surfaces 32, 34,the PV cells 6 are arranged along the first and second edge surfaces 28and 30. As shown, each of the PV cells 6 more particularly in thepresent embodiment has a width equaling the thickness 20, and extendsalong the entire respective one of the oppositely-oriented edge surfaces28, 30. The first and second edge surfaces 28, 30 at which the PV cells6 are located can also be referred to as longitudinal edge surfacessince they are at opposite ends of the length of the slab waveguide 18and are the edges toward which light is being directed by the waveguide.

Referring additionally to FIG. 2, a cross-sectional view of the solarconcentration section 4 of the solar energy device 2 (that is, the solarenergy device 2 with the PV cells 6 removed) in assembled (rather thanexploded form) is provided, which particularly illustrates exemplaryoperation of the solar concentration section 4 in channeling light tothe first and second edge surfaces 28, 30 along which the PV cells 6 areto be mounted. As shown, light rays (e.g., sunlight) 36 enter anexemplary one of the lenses 10 of the lens array 8 and, upon doing so,are focused by that lens. The focused light proceeds through the lowindex cladding layer 16 and subsequently into the slab waveguide 18,with the light then proceeding from the inner surface 22 of the slabwaveguide to the outer surface 24 of the slab waveguide. Ultimately, thefocused light reaches an exemplary one of the prism facets 26 locatedalong the outer surface 24 of the slab waveguide, with the focal pointof the focused light occurring at that prism facet.

Although the incident light rays 36 focused by the exemplary one of thelenses 10 and received by the exemplary one of the prism facets 26 isparticularly shown in FIG. 2, it will be understood that other lightrays (not shown) incident upon each of the other lenses 10 wouldsimilarly be focused by the respective lenses and proceed through thelow index cladding layer 16 and through the slab waveguide 18 to otherrespective ones of the prism facets (not shown).

The prism facets 26 in particular are reflective facets that areconfigured to reflect (or “inject”) the focused light back into the slabwaveguide 18 at sharp angles such that when the light reencounters thelow index cladding layer 16 it is again reflected into the slabwaveguide. That is, once the prism facets 26 have acted upon the focusedlight, the light reflected off of the prism facets experiences totalinternal reflection (TIR) or at least substantially experiences TIRwithin the slab waveguide 18 as far as the light's interaction with thelow index cladding layer 16, the outer surface 24 and the third andfourth edge surfaces 32, 34 (due to the reflective coating appliedthereto) is concerned. To the extent that TIR is only substantially (butnot exactly) achieved, a small portion of the light still escapes theslab waveguide 18 as a decoupling loss 31. Regardless, once light hasentered the slab waveguide 18 by way of the low index cladding layer 16,all or substantially all of the light continues to reflect repeatedlywithin the waveguide until it reaches either of the first or second edgesurfaces 28, 30. In the absence of the PV cells 6, light reaching theedge surfaces 28, 30 would escape from the slab waveguide 18 asillustrated in FIG. 2; however, in the presence of the PV cells 6, thelight reaching the edge surfaces 28, 30 enters the PV cells and isconverted into electricity.

The TIR experienced by light within the slab waveguide 18 is completelyindependent of wavelength and polarization over a wide range of anglesthat are steeper than the critical angle. The angle of incidence at thefirst and second edge surfaces 28, 30 is less than the critical angle,so the light can be emitted through those surfaces. In order to ensurethat all (or substantially all) of the light trapped within the slabwaveguide 18 is coupled into the PV cells 6, the PV cells typically havean anti-reflection coating (or an index-matching layer between thewaveguide and the surface of the PV cell). It should be noted that theoperation of the slab waveguide 18 is not perfectly efficient, since theprism facets 26 that reflect the light so that TIR occurs can also actto strip the light from the waveguide. However, in this regard, it issignificant that the diameter of the focal spots occurring at the prismfacets 26 is roughly one percent of the diameters of the lenses 10(e.g., a 1 mm diameter lens can produce approximately a 10 micron spot),such that the total area of the focal spot is 0.01% of the area of thelens, and such that the surface of the waveguide is 99.99% reflective(thus light can propagate for hundreds of lens diameters beforesignificant amounts of light are lost).

The shape and sizes of the prism facets 26 or other injection featuressuch as mirrored facets employed in any given embodiment can varydepending upon the embodiment (indeed, different ones of the prismfacets along the same waveguide can have different shapes/sizes). Often,the particular injection features employed will desirably be tailoredspecifically for the application. In at least one embodiment, the prism(or mirrored) facets 26 are symmetric, triangular in cross section, andcouple light equally to the left and the right as illustrated in FIG. 2.Such a shape is easy to fabricate due to the lack of sharp transitions.In another embodiment, the prism (or mirrored) facets 26 can havesawtooth-shaped features that reflect light primarily or entirely towardone or the other of the PV cells 6 at the opposite edge surfaces 28, 30.In some other embodiments, more than two PV cells are employed alongmore than two of the edge surfaces, or only one PV cell is employedalong only one of the edge surfaces. Further, while in some embodimentsthere is only a single PV cell along any given one of the edge surfaces,in other embodiments there are more than one PV cell along one or moreof the edge surfaces.

As noted above, it is desirable that a solar energy system employingboth solar concentrators and PV cells such as the solar energy system 2be easily manufactured so as to reduce manufacturing costs. Further,with respect to the present solar energy system 2, accurate alignment ofthe respective prism facets 26 relative to the respective lenses 10 isan important consideration in obtaining effective performance of thesolar energy system. While manual alignment of the prism facets 26relative to the lenses 10 is possible, this becomes more difficult asthe prism facets 26 become smaller, which (as discussed above) isdesirable to minimize the amount of light that escapes from the slabwaveguide 18. In view of these considerations, referring to FIG. 3, inat least some embodiments of the present invention, an automatedmanufacturing process 40 is employed to create the solar energy system2. In particular, as will be discussed below, in at least some suchembodiments, a “self-alignment” process is employed to form the prismfacets 26. Also as will be noted, by employing the manufacturing process40, it is particularly possible to manufacture solar energy systems 2(especially the solar concentration sections of those systems) in sheetsin a batch manner using rollers and other conventional mass-productiontechnologies, that is, in a roll-processing manufacturing process.

As shown in FIG. 3, the process 40 begins at a step 41 by applying asuperstrate 42, composed of acrylic or similar material, upon anassembly 44 including a slab waveguide portion upon which a low indexcladding layer has already been applied (such that the cladding layer isultimately positioned between the superstrate and the slab waveguideportion). This can be performed by way of rollers 46 as shown. Next, ata step 48, lens array embossing is performed by way of an embossmentroller 52 so as to form lenses 49 in the acrylic superstrate 42. Next,at a step 50, an ultraviolet-curable epoxy serving as a moldingfilm/photoresist 54 is further applied by a molding film applicationroller 56 along the outer surface of the assembly 44 (that is, thesurface which does not face the acrylic superstrate 42). Upon beingapplied, the molding film/photoresist 54 can be considered to be part ofthe slab waveguide portion of the assembly 44. Additionally, at a step58, a ruled prism master roller 60 is employed to emboss/stampintermediate prism facet formations 62 within the moldingfilm/photoresist 54.

Next, at a step 64, localized prism facets 66 are particularly formed inthe intermediate prism facet formations 62. The localized prism facets66 are formed in particular by shining light from a light source (ormultiple light sources) 68 through the lenses 49, where the light inparticular serves to expose apertures in the molding film/photoresist54. That is, the light causes certain portions of the moldingfilm/photoresist 54 that are desired as the localized prism facets 66 tobe cured. The light source 68 can be a deep blue 420 nm light, forexample, since this is the longest wavelength that will crosslink theepoxy and minimize the effect of chromatic aberrations from the lenses.Subsequently at a step 70, a solvent bath 72 removes excess uncuredfacet material (e.g., removes unused, uncured material of the moldingfilm/photoresist 54) such that only the localized prism facets remained(approximately 99.99 of the molding film/photoresist 54 is removed).

Subsequent to the step 70, additional steps (not shown) involve sprayingthe bottom surface of the waveguide (that is, the outer surface of theassembly 44 including the localized prism facets 66 with another thinlayer of low-index cladding material, depositing a metal mirror oncertain edge surface(s) of the waveguide (e.g., the edge surfacecorresponding to the surfaces 32, 34 mentioned above), and then mountingthe PV cells upon the overall assembly, particularly along the remaining(unmirrored) edge surface(s) of the slab waveguide (e.g., the edgesurfaces corresponding to the surfaces 28, 30 mentioned above).

By using the above-described process (or similar processes) ofmanufacture, it is possible to create solar energy systems such as thesolar energy system 2 of FIGS. 1-2 having a variety of dimensions andoptical characteristics. For example, the concentration power of thelenses 10 can vary depending upon the embodiment and, in one exemplaryembodiment, the concentration power of the lenses is 500 suns. Also, inone embodiment, the length of the slab waveguide 18 (that is, thedistance along which light is intended to flow through the waveguide,e.g., the distance between the two PV cells 6 at the edges 28, 30) canbe of any arbitrary length, for example, several meters long. Likewise,the width of the slab waveguide 18 (that is, the distance across theslab waveguide perpendicular to the distance along which light isintended to flow, and perpendicular to the thickness 20) can bearbitrarily large or small, for example, 500 millimeters oralternatively 1 meter. Also, the thickness 20 can be arbitrarily largeor small. Typically, it is desired that the thickness 20 be small,and/or that the thickness at least in part be determined by thecharacteristics (e.g., the concentration powers/focal lengths) of thelenses 10. In one embodiment, further for example, the lenses 10 areF/2.9 lenses and the thickness is only 6 mm (which is far less than forthin parabolic reflector optics).

A variety of other operational processes are also intended to beencompassed within the present invention in addition to that describedabove with respect to FIG. 3. For example, with respect to FIG. 4A, amodified version of the process 40, shown as a process 80, includes aslightly-different set of operational steps than those shown in FIG. 3.More particularly as shown, the process 80 begins at a step 82 with theaddition of low index cladding to one (e.g., the top) surface of a slabwaveguide, continues at a step 84 with the addition of a photosensitivepolymer molding agent to an additional, opposed (e.g., the bottom)surface of the slab waveguide, and further continues at a step 86 withthe formation of prism facets in the molding agent using a ruled master.Next, at a step 88, a reflective coating is placed onto the prismfacets, at a step 90 a lens array is attached to the low index cladding(e.g., attached to the top surface of the slab waveguide as modified toinclude the cladding), and at a step 92 the molding agent is exposed tolight via the lens array. Finally, at a step 94 mold development occurs,followed by remaining actions (e.g., attachment of the PV cells) thatresult in a final device at a step 96.

Further for example, FIG. 4B shows an additionally modified version ofthe process 80, shown as a process 100. As shown, the process 100includes steps 102-108 that respectively correspond to the steps 82-96of the process 80 respectively (except insofar as no step correspondingto the step 88 is included). Additionally, a step 101 shown to precedethe step 102 merely is indicative of the fact that a slab waveguide isprovided prior to the application of the low index cladding layer in thestep 102, and a step 98 is shown to be performed between the steps 106and 107, in which a reflective coating is applied to the slab waveguide(e.g., along edge surfaces such as the edge surfaces 32, 34 of FIG. 1).(The step 98 can be considered a substitute for the step 88 of FIG. 4A).

Additionally for example, FIG. 4C shows in yet another form a process110 for manufacturing a solar energy system such as the system 2 ofFIGS. 1-2. As shown, the process 110 begins at a step 111 by applying anun-crosslinked photopolymer coating onto a waveguide. Next, at a step111, a mold is applied to the photopolymer coating and additionally apull vacuum is applied. Subsequently, at a step 112, the waveguide,photopolymer coating and mold are baked with weight (pressure) applied,particularly pressure upon the mold tending to compress the assembly asshown. Further, at a step 113, the mold is removed. The removal of themold leaves the molded photopolymer coating exposed. The waveguide andmolded photopolymer coating is at this time then inverted.

Next, at a step 114, a lens array is attached to the waveguide along itsside that is opposite the side on which the photopolymer coating isattached. As illustrated particularly in FIG. 4C, ultraviolet light isfurther directed so as to be incident upon the lens array. Theultraviolet light in turn passes through the lens array and thewaveguide and then reaches the molded photopolymer coating. Due to thefocusing of the lenses of the lens array, the ultraviolet in particularonly reaches (is focused upon) specific portions of the moldedphotopolymer coating, and these specific portions of the coating in turnbecome crosslinked photopolymer. Next, at a step 115, a reflectivecoating is deposited upon the exposed outer surface (that is, thesurface not in contact with the waveguide) of the molded photopolymercoating, including the un-crosslinked and crosslinked portions. Finally,at a step 116, the overall assembly is heated above a glass transitiontemperature (Tg), the un-crosslinked portions of the photopolymercoating are removed (so as to complete formation of prism facets) and acompleted solar concentration section, suitable for implementation in asolar energy system such as the system 2, results.

The solar concentrators within the above-described solar energy systemsincluding the solar concentrator section 4 of the solar energy system 2can be referred to as passive solar concentrators. In such solarconcentrators, the refractive/reflective properties of the lenses andprism facets 10 are fixed such that variation in the angle of incidenceof incoming sunlight (or other light) as a function of movement of thesun (or otherwise) alters the degree of concentration and efficiency ofthe device. Referring to FIG. 5 in this regard, for example, across-sectional view of the solar energy system 2 of FIG. 1 is providedwith respect to which incident light 157 is shown to be tilted relativeto a normal axis 159 (which is perpendicular to the surfaces 22, 24 ofthe slab waveguide 18). As shown, if the incident light 157 is tilted inthis manner, the light after passing through a given one of the lenses10 of the lens array 8 is no longer directed toward the respective oneof the prism facets 26, but rather misses the prism facets. Assumingthat the outer surface 24 is transparent generally, that light can passcompletely out of the slab waveguide 18 such that it is no longerdirected to the PV cells 6 but rather simply is uncoupled light.

To reduce or minimize the amount of incident light that is lost due tothe light being imperfectly aligned with the solar energy system 2 asillustrated by FIG. 5, in at least some embodiments the solar energy ismodified, takes other forms, or can be operated in particular mannersthan as discussed above. In at least some embodiments, for example, toallow for enhanced performance of such a solar energy systemnotwithstanding variation in the angle of incidence of incoming light,the system in at least some embodiments is mounted upon (or otherwiseimplemented in conjunction with) an active alignment system.

Further, as noted above, in at least some additional embodiments, theprism facets 26 are configured to be more tolerant of variations in theincidence angles of light impinging the solar energy system. Indeed, inat least some such embodiments, the upward-facing lenses 10 canthemselves be used during the construction of the system 2 to identifyand form the location of the coupling prism facets 26, for example, asshown in the step 68 of FIG. 3. That is, while in some embodiments, theprism facets 26 that are formed in the manner described with respect toFIG. 3 are localized discrete facets intended to receive incoming lightalong a particular path, it is possible in other embodiments for theangle and intensity properties of the light used during the exposure tobe altered so as to form prism facets that are arcs or other structuresinstead of merely localized discrete facets. When appropriatelyconfigured, such arcs or other structures can direct light into thewaveguide 18 even though the incoming path of the light varies with thepath taken by the sun over the course of a day. Thus, through acustomized facet exposure/formation process to form such arcs and otherstructures, and the subsequent use of such arcs or other structures,which can be said to “mimic” the path of the sun, the daily collectionefficiency of the system 2 can be enhanced even when only using relaxedor no active solar tracking.

Further, in other embodiments of the present invention, it is envisionedthat certain physical characteristics of the solar concentrators, andparticularly the prism facets/injection features or coupling medium,will actively respond to variations in the angle of incidence ofincoming sunlight (or other light) and thus performance of the solarconcentrators will be enhanced, in the absence of (or in addition to)any active alignment system. The solar concentrators of suchembodiments, which can be referred to as reactive concentrators, operateby providing a large area region that can temporarily form (or reveal)prism facets/injection structures using a material that reacts to brightlight at or near the focus of a lens. This creates a local change in theoptical properties, which covers only a small fraction of the total areawithin the total guiding structure. As the sun's illumination anglechanges, the positions of these prism facets/injection features/defectspassively react and move along with it. Thus, such reactiveconcentrators do not require active alignment or tracking to capture andconvert specular sunlight into electricity.

Various embodiments of solar energy systems with reactive solarconcentrators are possible. As noted, in some embodiments, the sun'sheat and/or illumination is used to form the locations of the prismfacets. This can be in the form of thermal expansion or other mechanicalmotion to bring the prisms in close contact with the guiding layer. Inother embodiments, the prism facets are positioned just along the outersurface of the slab waveguide, just outside of that surface (that is,outside of the waveguide). An intermediate medium that responds to thelocation/intensity of the sun causes a localized physical change in therefractive index at the point of focus allowing light that is reflectedoff the prisms to be coupled into the high-index guiding slab waveguide.A localized high refractive index surrounded by a low-index cladding isdesirable (or necessary) for the purpose of allowing the prism toencounter incoming light once and not adversely strip already guidedlight.

Depending upon the embodiment, several potential phenomena are availableto generate the necessary localized index change. In at least someembodiments, a colloidal suspension of high index nanoparticles in alower index fluid similar in optical properties to the outer cladding isprovided. The particles can be smaller in size than the wavelength oflight, and therefore seen as average and not individual scatteringparticles. An accumulation of high index particles causes the perceivedindex of refraction to rise creating the coupling window between thereflective prism facets and the guiding slab while still maintaining thelower-index cladding surround. One method for initiating this perceivedindex increase is using optical trapping forces inherent to highillumination flux. Other embodiments can incorporate photoconductive orweakly photovoltaic polymers which generate an electric field in thepresence of intense illumination. The resulting field can exert forceson the high index particles causing them to migrate towards the areas ofmaximum flux, generally occurring at the point focus of each lens in thearray. The system is still reactive in that the polymer can be placedeverywhere behind the guiding slab and not require individuallypatterned electrodes. Other optically induced physical changes may aidin the coupling of light such as photochromic, photothermal or phasechange materials.

Referring to FIG. 6, a side elevation view of one exemplary embodimentof a solar energy system 122 employing a reactive concentrator section124 in addition to PV cells 126 is shown. As shown, the reactiveconcentrator section 124 in particular is formed from several layersstacked together. On the top is an array 128 of lenses 130 used to formfocal points from the incident sunlight. A low index cladding layer 136exists just below the lenses 130 followed by a high index guiding layer(e.g., a slab waveguide layer or core) 138. Lastly a mirror (reflective)microstructure 140 sits below the high index guiding layer 138 with agap 142 filled by a colloid in suspension (colloidal suspension) 144.The colloid 144 contains a low index fluid or gel with high indexparticles evenly dispersed within, achieving an average index similar tothe cladding layer 136 found above the guiding layer 138. The PV cells126 are placed at edge surfaces of the high index guiding layer 138 aswith the solar energy system 2 of FIGS. 1-2 (also, while not shown,reflective coatings are placed on the other edge surfaces).

Turning to FIG. 7, the solar energy system 122 can be understood asoperating generally according to a process 150. Upon providing of thesolar energy system 122 at a step 152, sunlight is incident upon thesolar concentrator section 124 at a step 154. Upon illumination, thelenses 130 focus the light so that it passes through all of the layersof the solar concentrator section 124 (e.g., the layers 136 and 138) soas to be incident on the mirror microstructure 140 as spots. Next, at astep 156, with high illumination flux, significant optical trappingforces are exerted on the particles suspended in the colloid 144.Particles outside the illumination cone undergo Brownian motion causingthem to constantly migrate. Over time, more particles can be trapped bythe illumination causing a local grouping of high index particles. Sinceeach is significantly smaller than the wavelength of light, the sunlightonly sees the average index of refraction which is increased by theaccumulation of particles. Thus, a high index channel is created forlight to couple into the guiding layer, and prism facets are createdwithin the colloid 144. As discussed in relation to the solar energysystem 2 of FIGS. 1-2, the coupling windows should remain small toreduce the probability of a ray which is already guided from seeing themicrostructure beneath and scattering out of the core (this willultimately limit the distance light can be guided and can be a mainconsideration of design).

Upon completion of the step 156, the angled prism facets of the mirroror grating reflect light at angles necessary to achieve TIR, such thatthe light reflected by the prism facets couple directly into the layer138 (rather than refracting into and out of the various layers), andeventually then are channeled toward the PV cells 126, at whichelectrical power is then generated, as indicated by a step 158. Further,since the colloidal accumulation is optically induced and occurslocally, the system is able to react to the position of the sun. Thatis, as indicated by a step 160, over time the angle of incidence of thesunlight upon the lenses 130 changes. When this occurs, the colloid 144further responds so as to result in modified prism facets at the step156. Thus, continued movement of the sunlight results in repeatedperformance of the steps 156, 158 and 160 (on a continuous basis).

In at least some embodiments, the colloid 144 can involve the suspensionof titanium dioxide (TiO₂) particles. These are subwavelength particleswith a very high index of refraction and have potential to be easilytrapped and manipulated with sunlight. The particles will likely becoated with silica, etc., to avoid clumping due to Vander Waals forces.In at least one such embodiment, the colloid 144 includes both thetitanium dioxide particles, which are nanoscale, high dielectric indexparticles, and also dense but low index of refraction fluoropolymermaterial, within which the particles are contained. During operation,the photosensitive material repeatedly senses and responds to changes inelectric fields of portions of the light, by drawing in some of the highdielectric index particles (that is, due to the light exposure, some ofthe particles move from one location to another within the overallcolloid) so as to achieve optical trapping. In other embodiments, othermaterials can be used as the colloid. Also, the colloidal solution isonly one of many potential methods for creating a high index window tocouple to the waveguide/core. Other static and mechanical possibilitiesexist as well as active electrical addressing. Phenomena includingdielectrophoresis can also be utilized to manipulate the location ofparticles. It will be further understood that the solar energy system122 of FIG. 6 employing the reactive solar concentrator 124 can bemanufactured using processes similar to (albeit not identical to) theprocesses described above with respect to FIGS. 3-4B.

Notwithstanding the above discussion, in still additional embodiments ofthe present invention various techniques can be employed by which thesolar energy system, rather than using full active tracking, insteademploys micro-tracking features in which one or more components of thesolar energy system are moved slightly relative to other components soas to achieve improved performance by the solar energy system in termsof its ability to receive and couple light to the PV cells 6 even whenthat light is incident in a tilted manner and/or varies in its angle ofincidence over time. These slight movements can involve, for example,both lateral movements (that is, movements of the waveguide side-to-sidebut not toward or away from a lens array), as well as vertical movements(that is, movements of the waveguide toward or away from a lens array).Turning to FIG. 8 in particular, in one such embodiment a solar energysystem 162 includes not only one or more PV cells 6 and the solarconcentration section 4 with the slab waveguide 18 and the lens array 8with the lenses 10 (as well as the prism facets 26) of the solar energysystem 2 discussed above, but also includes first, second and thirdadditional lens arrays 166, 167 and 168.

As shown, each of the lens arrays 166-168 includes a plurality ofindividual lenses 169. More particularly, the lenses of the first,second and third lens arrays 166, 167 and 168 are respectively arrangedalong first, second and third planes parallel to the plane along whichthe lens array 8 is arranged, with the third, second and first planesbeing positioned successively outwardly away from the lens array 8. Inthe present embodiment, each of the lenses 169 of each of the lensarrays 166-168 is identical. However, in other embodiments the lenses ofthe different lens arrays 166-168 can be different from one another and,indeed, in at least some embodiments different lenses of a given one ofthe lens arrays 166, 167 and/or 168 can also differ from one another. Inthe present embodiment, the lenses 169 of the different lens arrays166-168 can be considered micro-lens arrays since the lenses aretypically small in diameter (and equal in diameter to the lenses 10 ofthe lens array 8).

The lenses 169 of the lens arrays 166-168 are intended to be moveablerelative to one another and/or the lenses 10 of the lens array 8 suchthat incident light that is incident upon the solar energy system 162(and particularly incident upon the lenses of the lens array 166) at avariety of angles can still be ultimately directed in a manner so thatthe light is normally incident upon the lenses 10 of the lens array 8,that is, parallel or substantially parallel to the normal axis 159. Inthe present embodiment, the lens array 167 in particular is moveablealong an axis of movement represented by an arrow 170 that is parallelto the inner and outer surfaces 22, 24 of the slab waveguide 18 and thusperpendicular to the normal axis 159. By appropriately adjusting thesecond lens array 167 relative to the other lens arrays 166, 168 (and8), incident light 171 that is tilted relative to the normal axis 159thus can be redirected so as to be normal upon the lens array 8 in amanner that is parallel or substantially parallel to the normal axis159. Thus, even though the incident light 171 is tilted, light iseffectively received and coupled by the solar concentration section 4 asif it were normally received and thus the solar concentration section isable achieve effective coupling of the light to the PV cells 6.

The embodiment shown in FIG. 8 employs a triplet of micro-lens arrayswhere the second lens array 167 in particular serves as a field lensthat increases the fill factor at the output of the lens arrays (thatis, the light as it proceeds toward the lens array 8). Nevertheless, inother embodiments other lens arrangements can also be employed. Forexample, in one other embodiment, only two lens arrays are employed(albeit such an embodiment can suffer from somewhat limited steeringrange and increased number of surface reflections, with the limitedsteering range being partly the result of the arising of spurious rays).In other embodiments, more than two lens arrays are present. Also,depending upon the embodiment, not merely the second lens array 167 butalso (or instead) one or another of the lens arrays 166, 168 (and/or 8)can be moved. By appropriately moving such one or more lens arrays overtime, changes in the direction of incident light as can be associatedwith movement of the sun over the course of a day (or as may occur forother reasons as well) can be largely compensated for, and thus,operation of the solar energy system 162 can continue unimpeded orlargely unimpeded throughout the day.

Turning next to FIG. 9, an additional embodiment of a solar energysystem 172 also employs a micro-tracking capability that differs fromthat of FIG. 8. In the embodiment of FIG. 9, the solar energy system 172can be understood to include the both the lens array 8 as well as theadditional waveguide portions 19 of the solar concentration section 4 ofthe solar energy system 2 of FIG. 1 (e.g., the waveguide 18 with theprism facets 26, as well as possibly the cladding layer 16). However, incontrast to the solar concentration section 4, in this embodiment thelens array 8 is moveable relative to the additional waveguide portions19 of the solar concentration section, such that the additionalwaveguide portions can be moved relative to the lens array 8 back andforth along a direction indicated by an arrow 177, the directionrepresented by the arrow 177 being parallel to the outer and innersurfaces 22 and 24 of the waveguide 18. In at least some suchembodiments, a space 178 between the lens array 8 and the additionalwaveguide portions 19 can exist to facilitate such movement (such spacecan be filled with air or other cladding). By appropriately moving theadditional waveguide portions 19 (this movement can involve a slidingmovement along a bottom surface of the lens array 8) the additionalwaveguide portions can be positioned relative to the lenses 10 such thatincident light 174 that is incident upon the lenses in a tilted mannerrelative to the normal axis 159 still is focused upon appropriate ones(in this example, an appropriate one) of the prism facets 26. Thus, eventhought the incident light 174 is tilted, the light ultimate experiencesTIR within the waveguide 18 and is directed to the PV cells 6.

As discussed with respect to FIG. 8, it will be understood that theappropriate positioning of the additional waveguide portions 19 relativeto the lens array 8 will vary depending upon the particular angle ofincidence of the incident light 174 relative to the normal axis 159 andthus, as that angle of incidence changes (e.g., again due to movement ofthe sun during the course of the day or for some other reason) therelative positioning of the additional waveguide portions relative tothe lens array 8 will need to be appropriately modified so that theincident light continues to be directed towards one or more of the prismfacets 26. Such appropriate positioning can be governed by a controllersuch as a microprocessor (not shown) that receives signals from one ormore light sensors (also not shown) that detect the angle(s) ofincidence of the incident light 174 (or at least predominant orsubstantial component(s) of that light) and based upon such receivedsignals in turn adjusts the relative positioning of the additionalwaveguide portions 19 vis-à-vis the lens array 8. In general, the amountof shifting of the additional waveguide portions 19 relative to the lensarray 8 will correspond to the degree of tilt in the incident light;increased tilt will typically require increased amount of shifting.Although the amount of shifting required to achieve a desired effectwill vary depending upon the embodiment, the amount of shifting willoften be quite small (e.g., on the order of 1 millimeter or less).

Turning to FIG. 10, in yet another embodiment of a solar energy device182, not only is there present the lens array 8 as well as theadditional waveguide portions 19 (and possibly the space 178 separatingthe two), but also there is an additional diffuse light collector 184(which for example can be a large area PV cell panel or solar-thermalpanel) that is positioned outside of the additional waveguide portionsalongside the outer surface 24. Given such an arrangement, incidentlight 186 that is well-collimated is directed towards the prism facets26 (particularly assuming that the additional waveguide portions 19 areappropriately aligned relative to the lens array 8), while otherdiffused light 188 that is incident upon the lens array 8 is notdirected towards the prism facets 26 but instead is allowed to passthrough the slab waveguide 18 completely and so is received at thediffuse light collector 184. Thus, well-collimated incident light isprovided to the PV cells 6 while diffuse light is received at thediffuse light collector 184. Notwithstanding the effectiveness of thesolar energy systems 162, 172, 182 discussed above with respect to FIGS.8-10, the effectiveness of such solar energy systems can still besomewhat limited depending upon field curvature 178 as illustrated inFIG. 9.

Next, referring to FIGS. 11-12, a further exemplary solar energy system192 is shown in two different operational positions. As shown, the solarenergy system 192 includes waveguide portions 194 that are similar tothe additional waveguide portions 19 discussed above, and thatparticularly include a slab waveguide 195 and prism facets 193 by whichlight is directed to PV cells 196 at opposite ends of the slabwaveguide. Additionally, the solar energy system 192 further includes alens array 198 having a plurality of lenses 199. Further, as in thesolar energy system 172, the waveguide portions 194 (and PV cells 196mounted in relation thereto) are laterally shiftable relative to thelens array 198. However, in contrast with the solar energy system 172,the solar energy system 192 is configured to receive incident light thatfirst impinges the system at an outer surface 191 of the waveguideportions 194 along which the prism facets 193 are located rather than atthe lenses 199 of the lens array 198. More particularly as shown,incident light 200 passes through the outer surface 191, proceedsthrough the slab waveguide 195 and through an inner surface 201 of theslab waveguide (again at which can be provided a cladding layer), thenthrough an air gap (or other possible cladding) 203 between thewaveguide portions 194 and the lens array 198, and then through the lensarray to the lenses 199. Upon reaching the lenses 199, the light is thenreflected by the lenses back generally in the opposite direction towardappropriate ones of (in this case, one of) the prism facets 193, atwhich point the light experiences TIR and is directed to the PV cells196. It will be understood that, to achieve operation in theabove-described manner, the outer surface 191 of the slab waveguide 195is substantially transparent, while the lenses 199 are mirrors (or arelenses with a mirror coating applied thereto). The lenses 199 in thepresent embodiment can be more appropriately termed micro-mirrors giventheir small size.

While FIG. 11 shows the light 200 incident upon the waveguide portions194 to be normal to waveguide portions (that is, perpendicular to theouter and inner surfaces 191, 201), the solar energy system 192 againallows for incident light that is tilted to also be captured anddirected towards the PV cells 196. In particularly referring to FIG. 12,tilted incident light 189 also can be successfully directed to the PVcells 196 by laterally shifting the waveguide portions 194 relative tothe lens array 198 by an appropriate amount along a direction (back andforth along the direction) represented by an arrow 187. It shouldfurther be noted that the use of the solar energy system 192 isparticularly advantageous insofar as, due to the flatness (and typicallyrobustness) of the outer surface 191, the solar energy system realizesimproved durability of packaging and ease of cleaning.

Turning to FIGS. 13 and 14, a further solar energy system 202 is shownin accordance with another exemplary embodiment of the present inventionin which slight movements of system components allow for tilted incidentlight to be captured at the PV cells of the device. The solar energysystem 202, for reasons that will be understood in view of thediscussion below, can be particularly termed a micro-catadioptricconcentrator system. Referring particularly to FIG. 13, the solar energysystem 202 among other things includes waveguide portions 204 includinga slab waveguide 205 having first and second surfaces 206 and 208 thatare opposed to one another on opposite sides of the waveguide, andfurther having prism facets 210 that are positioned along the surface206. PV cells (one of which is shown) 212 are positioned at one (asshown) or more edge surfaces of the waveguide 205. Additionally, thesystem 202 also includes a lenslet array 214 that is positioned along(and spaced apart from) the first surface 206 of the waveguide 205 and amicro-mirror array 216 that is positioned along (and spaced apart from)the second surface 208 of the waveguide. In the present embodiment, airgaps (or other cladding) 218 are provided between the lenslet array 214and the first surface 206 as well as between the micro-mirror array 216and the second surface 208.

As with the solar energy system 192 and 172 discussed above, thewaveguide portions 204 and associated components (e.g., the PV cells212) can be laterally shifted relative to the lens components of thedevice, namely, laterally shifted relative to both the lenslet array 214and the micro-mirror array 216 back and forth along a directionrepresented by an arrow 220. When in the position shown in FIG. 13,incident light 222 that is parallel to an axis 230 normal to the slabwaveguide 205 (that is, perpendicular to the surfaces 206, 208)initially impinges the solar energy system 202 at the outer surface ofthe lenslet array 214, after which it passes through the lenslet array(which causes some focusing of the light), through the air gap 218between that lenslet array and the waveguide portions 204, through thewaveguide portions including the slab waveguide 205, through theadditional air gap 218 between the waveguide portions and themicro-mirror array 216 and up to an outer surface 224 of themicro-mirror array. As with the solar energy system 192, at this pointthe light is reflected by the micro-mirror array 216 back inward towardsthe slab waveguide 205 and eventually passes through the slab waveguideand to appropriate ones of (in this example, one of) the prism facets210, as a result of which the light experiences TIR and proceeds to thePV cells 212.

Further, as shown in FIG. 14, with an appropriate lateral shifting ofthe waveguide portions 204 (and PV cells 212) relative to the lensletarray 214 and the micro-mirror array 216, incident light 226 that istilted relative to the axis 230 is largely also directed eventually tothe PV cells 212. As illustrated, while most of the tilted incidentlight 226 eventually finds its way to the PV cells 212, a small amountof light is vignetted light 231 and escapes the system 202. As withrespect to the embodiments discussed with reference to FIGS. 8-12, thesolar energy system 202 can achieve successful coupling of incidentlight to the PV cells 212 for incident light that is tilted at a varietyof angles, it being understood that as the degree of tilting increasesthe degree of shifting will also need to increase. It will be understoodthat, in any given embodiment, it is possible for one or more actuatorsto be controlled to move waveguide portions relative to lens arraystructures (including multiple structures such as both the lenslet array214 and the micro-mirror array 216), with those lens array structuresbeing stationary, or vice-versa, or to move all of the differentcomponents in various directions.

In the above-described embodiments of solar energy systems, PV cells arepositioned along edges of slab waveguides so as to receive lightdirected by the slab waveguides to and outward form those edges.However, the confining of light at known angles within waveguides as isachieved in such solar energy systems does not mandate that PV cells beoriented in such manners to receive that light. Rather, depending uponthe embodiment, additional arrangements are possible that allow forrepositioning of PV cells or light extraction in a manner that achievesadditional concentration. More particularly, referring now to FIGS.15-18, solar energy systems such as those discussed above can bemodified in additional manners that facilitate the communication oflight within the slab waveguides to PV cells that are intended toreceive that light that are positioned in a variety of manners, and/orfacilitate light extraction in a manner by which greater concentrationis achieved.

For example, with respect to FIG. 15, a modified version of the solarconcentration section 4 of the solar energy system 2 of FIG. 2, referredto as a solar concentration section 234, is shown. The solarconcentration section 234 in particular has, as shown, not only a lensarray 232 with a plurality of lenses 236 as well as a slab(uniform-thickness) waveguide 238 having an outer surface 240, an innersurface 242 and a plurality of prism facets 246, but also additionally afold prism 248 positioned at an edge 250. The fold prism 248 serves torotate the light emanating from the waveguide 238 from lateral todownward propagation (e.g., a 90 degree rotation), which allows a PVcell (not shown) to be placed underneath the waveguide so as to beparallel to the outer surface 240 of the waveguide 238 rather than alongthe edge 250 of the waveguide.

Referring additionally to FIG. 16, through the use of multiple solarenergy systems each employing the solar concentration section 234 ofFIG. 15, further concentration of light for reception by a PV cell(and/or ease of manufacture of the overall solar energy system) can beachieved. For example, by positioning two of the solar concentrationsections 234 end-to-end, where the sections include respective foldprisms 248, light from the two solar concentration sections 234 can bedirected to a single PV cell 251. Thus, only the single PV cell 251 isnecessary for capturing light from two of the sections 234. It will beunderstood that, in further embodiments, more than two (e.g., 4) solarconcentration sections can effectively share the same PV cell in asimilar manner.

Referring to FIG. 17, portions of another exemplary solar energy systemare shown. In this embodiment, the solar energy system includes twosolar concentration sections 254. As with the solar concentrationsection 234, each of the solar concentration sections 254 again includesa respective lens array 252 with a respective plurality of lenses 256 aswell as a respective slab (uniform-thickness) waveguide 258 having arespective inner surface 262 and a respective outer surface 260, alongwhich are formed a respective plurality of prism facets (not shown).Each solar concentration section 234 can have a thickness (that is, asmeasured between the outer surface of the lens array 252 and the outersurface 260) of, for example, 2 millimeters. Additionally, positionedbetween the solar concentration sections 254 is a curved mirrorreflector 268 oriented so as to be concave toward the plane of the innersurfaces 262. The curved mirror reflector 268 can be any of a variety ofdifferent curved shapes depending upon the embodiment and, for example,can be an aspheric mirror reflector or a curved mirror reflector. In thepresent embodiment, the curved mirror reflector 268 extends outward awayfrom the waveguides 258 farther than do the lens arrays 252, althoughthis need not be the case in all embodiments.

The curved mirror reflector 268 receives light provided to it from thewaveguides 258 as that light proceeds out of the ends of the waveguides,and in turn focuses the light toward a central location 266 between thesolar concentration sections 254 generally along the plane determinedthe outer surfaces 260. Again, as with respect to the system of FIG. 16,a packaged PV cell 270 can be positioned at this central location asshown so as to receive the focused, concentrated light. Thus, both thefold prisms 248 and the curved mirror reflector 268 of FIGS. 16 and 17,respectively, serve to rotate the light emanating from the waveguides238, 258, from lateral to downward propagation, albeit the curved mirrorreflector provides the added benefit of further concentrating the lightfor receipt by the PV cell 270. Such concentration not only allowspotentially the use of a smaller PV cell (which is desirable, due to thecost of larger PV cells), but also allows the PV cell to be moreeffectively operated (typically, PV cells achieve greater efficiency ofoperation upon receiving more intense light).

In view of the embodiments of FIGS. 15-17, it should be further evidentthat, depending upon the embodiment, two (or more) opposing solarconcentration sections can be joined so as to couple bi-directional (ormulti-directional) light into a common PV cell. Also, symmetric couplersenable linear arrays of micro-optic concentrators. Referringadditionally to FIG. 18, for example, a planar concentrator array 272 isshown in cutaway to include six solar concentration sections 254 of thetype shown in FIG. 17 (the waveguides 258 being shown in particular) andfour of the curved mirror reflectors 268, with each of the reflectorsbeing positioned between two corresponding ones of the solarconcentration sections (where to of those sections are between two ofthe reflectors). The curved mirror reflectors 268 direct light receivedfrom the solar concentration sections to PV cells (not shown) positionedbeneath four different curved mirror reflectors 268. Notwithstanding theparticular structure shown, it will be understood that any arbitrarynumber of solar concentration sections and curved mirror reflectors ofthis type can be assembled into a larger structure in this manner. Sucha structure is not only easy and convenient to fabricate but also insome cases can be easily stored (e.g., the planar array can potentiallybe rolled up).

As already mentioned, increased concentration of light onto a given PVcell can improve the performance of the PV cell. Output coupler designssuch as those discussed above using curved (e.g., aspheric or parabolic)mirrors (instead of planar fold prisms) are particularly capable ofremapping guided ray angles and focusing light onto a given PV cell.Additionally it can be noted that reflective surfaces with optical powerenable another stage of concentration in addition to the increased fluxgained from coupling light into the waveguide. Combining two methods ofconcentration allows the system to efficiently reach high levels of fluxneeded for multi junction PV cells. Many potential designs have beenexplored and vary based on the waveguide modes, yet most embodimentsutilize at least one curved mirror to collect diverging light as itleaves the waveguide.

An additional factor influencing the performance of a PV cell is thedegree to which the PV cell is suited to receiving the particular lightspectra that are provided to it. Turning next to FIGS. 19-23, in atleast some embodiments of the present invention, solar energy systemsare configured to differentiate between/among different light spectraand to direct different light components to different PV cells that areparticularly well-suited for receiving those respective lightcomponents. In at least some such embodiments, dielectric mirrors areincorporated into the solar concentrator design to split broad spectrumillumination into multiple bands for collection using specialized PVcells.

Referring to FIG. 19, in one such embodiment a solar concentrationsection 274 is employed. The solar concentration section 274, as shown,is similar to the solar concentration section 4 of FIG. 2 insofar as itemploys a lens array 276 having multiple lenses 278 placed adjacent to aslab waveguide 280. The slab waveguide 280 can, as was the case with theslab waveguide 18 of FIG. 2, include inner and outer surfaces 282 and284, respectively, with the inner surface 282 being adjacent to the lensarray 276 (it being further understood that a low index cladding layersuch as the layer 16 of FIG. 1 serves as this inner surface 282), andprism facets 286 (two of which are shown) being formed along the outersurface 284. PV cells (not shown) can be provided along outer edges 288and 289 of the slab waveguide 280. In contrast to the solarconcentration section 4, however, the solar concentration section 274additionally includes first and second dichroic mirrors 290 and 291 thatare respectively positioned along the first and second edges 288 and289, respectively (and which would therefore be positioned between thoseedges and any PV cells intended to receive light emanating through thoseedges).

As shown in FIG. 19, the dichroic mirrors 290, 291 are particularlyconfigured to pass certain way lengths of light and to reflect otherwavelengths of light. In the present example, first incident light 292of wavelength λ₁ (shown in dashed lines), upon impinging the lenses 278and passing into the slab waveguide 280 and being reflected by arespective one of the prism facets 286, experiences TIR within the slabwaveguide 280 and can proceed in either direction towards the first edge288 or the second edge 289. However, assuming that the dichroic mirror291 is reflective with respect to light of wavelength λ₁, any such lightthat arrives at the second edge 289 is consequently reflected by thedichroic mirror 291 and thus proceeds in the opposite direction towardthe first edge 288. Assuming that the first dichroic mirror 290 isconfigured to allow light of wavelength λ₁ to pass through that dichroicmirror, all of the light of that wavelength then proceeds out of thefirst edge 288 and through that dichroic mirror 290. To the extent thata PV cell (not shown) is positioned on the opposite side of thatdichroic mirror 290, that PV cell only receives light of the wavelengthλ₁. Assuming that such PV cell is selected so as to be particularlysuited for receiving light of this wavelength, the efficiency ofoperation of the PV cell can be maximized.

In contrast, with respect to second light 293 of wavelength λ₂ that isincident upon the lenses 278 (shown in solid lines), that light also canproceed in through the lenses and into the slab waveguide where itexperiences TIR due to interaction with the prism facets 286. However,in this case, the first dichroic mirror 290 is configured to reflectlight of the wavelength of the second light (λ₂) while the seconddichroic mirror 291 is configured to pass such light. Thus, all of thesecond light of the wavelength λ₂ only passes out of the waveguidethrough the edge 289 through the dichroic mirror 291 and, upon makingsuch passage, can be received by a PV cell that desirably is suited forreceiving light of that frequency.

The above-described features of the solar concentration section 274 ofFIG. 19, in which light is selectively reflected or passed at the edges(exit apertures) of a waveguide depending upon the wavelength of thelight, can be further combined with additional light-selective operationas shown in FIG. 20. More particularly, as shown in FIG. 20, anadditional embodiment of a solar concentrations section 294 includes notonly a lens array 296 with lenses 298 but also a first waveguide 300 anda second waveguide 301. The first waveguide 300 has a first surface 302and a second surface 304, where the first surface 302 is in contact withthe lens array 296 and the second surface 304 is in contact with thesecond waveguide 301. The second waveguide 301 includes a first surface305 that is an outermost surface of the solar concentration section 294and additionally a second surface 306 that is in contact with the secondsurface 304. The first surface 302 of the first waveguide 300 can beformed by a low index cladding layer such as the cladding layer 16 ofFIG. 1. However, in contrast to the embodiment of FIGS. 1-2, prismfacets 308 (two of which are shown) are formed not along the secondsurface 304 of the waveguide 300 but rather along the first surface 302that is in contact with the lens array 296.

Instead of placing prism facets at the second surface 304, that surfaceinstead is where a dichroic mirror (as well as possibly another claddinglayer) is formed and, for purposes of the description below, the secondsurface 304 is considered to be such a dichroic mirror (albeit thesecond surface 306 of the second waveguide 301 or both of the surfaces304, 306, can also be considered to be or include such a mirror). As forthe second waveguide 301, it also has prism facets 310, two of which areshown, formed along the first (outer) surface 305. Additionally asshown, at each of the longitudinal edges of the first and secondwaveguides 300, 301, further dichroic mirrors are placed in the samemanner as was described with respect to FIG. 19. Thus, at a right edge(as shown in FIG. 1) of the first waveguide 300 a first dichroic mirror311 is positioned while at a left edge of that same waveguide a seconddichroic mirror 312 is positioned. Likewise, at a right edge of thesecond waveguide 301 a third dichroic mirror 313 is positioned while ata left edge of that waveguide a fourth dichroic mirror 314 ispositioned.

Given the above-described arrangement, the solar concentration section294 is capable of differentiating among four different types of lightand directing those respective types of light to four different PV cellsrespectively. More particularly, first light 315 of wavelength λ₁ thatis incident upon the lenses 298, upon passing through the lens array 296and passing into the first waveguide 300, is reflected by the dichroicmirror 304 and consequently reflected back up to appropriate ones of (inthis example, one of) the prism facets 308 associated with that firstwaveguide. Likewise, second light 316 of wavelength λ₂ (shown in dashedlines) upon passing into and through the lens array 296 and into thefirst waveguide 300 similarly is reflected by the dichroic mirror 304and received at the prism facets 308. Upon reaching the prism facets308, each of the first and second light 315, 316, experiences TIR and isreflected within the first waveguide 300. Due to the additionaloperation of the first and second dichroic mirrors 311, 312 (insubstantially the same manner as was discussed with respect to FIG. 19),however, the first light of wavelength λ₁ is reflected by the seconddichroic mirror 312 so that it cannot pass out of the waveguide 300 atits left edge, but instead all of the first light passes through thefirst dichroic mirror 311 and thus exits the waveguide through its rightedge. Conversely, the second light 316 of wavelength λ₂ is precludedfrom exiting the first waveguide 300 at its right edge associated withthe first dichroic mirror 311, at which such light is reflected, but isinstead able to exit the first waveguide at its left edge at which islocated the second dichroic mirror 312, which passes that light.

In contrast to the first and second light 315, 316 that is reflected bythe dichroic mirror 304, both third light 317 of wavelength λ₃ andfourth light 318 of wavelength λ₄, upon entering the lens array 296 andpassing through the first waveguide 300, are able to pass through thatdichroic mirror and into the second waveguide 301. Upon passing into thesecond waveguide 301, the focused light 317, 318 reaches the prismfacets 310, at which that light experiences TIR. Due to the presence ofthe dichroic mirror 304 (and possibly due to any further effect of anyother layer such as a low index cladding layer at the second surface306, etc.), the third and fourth light cannot re-enter the firstwaveguide 300. Rather, due to the operation of the third and fourthdichroic mirrors 313, 314, the third light 317 is reflected at the leftedge of the waveguide 301 and only passes out of that waveguide at itsright edge by way of the third dichroic mirror 313, while the fourthlight 318 is reflected at the right edge of the waveguide 301 and onlypasses out of that waveguide at the left edge by way of the fourthdichroic mirror 314. Thus, given the embodiment shown in FIG. 20,incident light can be separated successfully into four different lightcomponents λ₁, λ₂, λ₃ and λ₄, which respectively exit the solarconcentration section at four different locations. Assuming thatrespective PV cells are placed adjacent to the respective dichroicmirrors 311-314 (or otherwise in position so as to receive lightemanating through those respective dichroic mirrors) that are suited forreceiving the particular light components emanating from thoserespective dichroic mirrors, enhanced operation of the PV cells and thusof the entire solar energy system 294 can be achieved.

Referring next to FIG. 21, another exemplary solar concentration section324 is shown in which incident light 332 is separated into differentlight components suitable for receipt by different PV cells. As shown,the solar concentration section 324 of FIG. 21 like the solarconcentration section 294 of FIG. 20 includes a first waveguide 320,which can be, for example, an infrared waveguide, and a second waveguide321, which can for example be a visible waveguide (again, each of thewaveguides can include appropriate cladding along its outer surfaces soas to form the waveguides; also, there can be in some cases a planarfirst surface anti-reflective coating applied to various surfaces of thesolar concentration section 324). In this embodiment, however, ratherthan employing a lens array that receives incident light prior to thatincident light being transmitted to the waveguides, the solarconcentration section 324 instead employs a lens array 322 that ispositioned in between the first and second waveguides 320, 321. Moreparticularly as shown, the lens array 322 includes a first lens subarray326 that includes a plurality of lenses 328 that are directed concave uptoward the first waveguide 320 and a second lens subarray 327 having aplurality of lenses 329 that are directed concave down towards thesecond waveguide 321. As shown, the second lens subarray 327 is thuscloser to the second waveguide 321 than the first waveguide 320, and thefirst lens subarray 326 is thus closer to the first waveguide 320 thanthe second waveguide 321, where a space 330 exists between the first andsecond lens subarrays.

Further as shown, the first lens subarray 326 more particularly iscoated with a dichroic coating such that the lenses 328 of that subarrayserve as reflective lenses (or mirrors) in relation to infrared lightwhile passing non-infrared (and in particular visible) light. Incontrast, the lenses 329 of the second lens subarray 327 are not coatedwith any dichroic coating but merely serve as refractive lenses for anylight (and particularly visible light) that reaches those lenses afterpassing through the reflective lenses of the first lens subarray 326.Given this arrangement, upon incident light 332 impinging the solarconcentration section 324 via an outer surface of 334 of the firstwaveguide 320, that light proceeds through the first waveguide 320 andinto the lens array 322. Infrared light components of the incident light332 are reflected by the lenses 328 of the first lens subarray 326 and,due to the focusing of those lenses, arrive at prism facets 336 formedalong the outer surface 334 of the first waveguide. Upon being reflectedat those prism facets 336, the infrared light experiences TIR andproceeds to the edges of the waveguide where the light can then proceedto PV cells (not shown).

By comparison, other light and particularly visible light entering intoand passing through the first waveguide 320 passes through the lenses328 of the first lens subarray 326 and into the lenses 329 of the secondlens subarray 327. This light is then focused so as to reach prismfacets 338 along an outer surface 340 of the second waveguide 321. Uponreaching the prism facets 338, the visible light experiences TIR andthus proceeds within the waveguide 321 to edges at which the light canexit the waveguide and be received by PV cells (again not shown). Itshould be noted that the embodiment of FIG. 21 is capable of achieving aunique lens power and concentration for each light band provided,assuming that there is normal incidence upon the dichotic reflectors.

Various combinations of two or more of the features described above canalso be encompassed in additional embodiments of the present invention.For example, as shown in FIG. 22, in one embodiment a solarconcentration section 344 is substantially identical to the solarconcentration section 294 of FIG. 20 insofar as it includes a lens array346, a first waveguide 350 and a second waveguide 351, along with adichroic mirror 348 positioned in between the two waveguides. Again,given this design, when incident light 349 impinges the solarconcentration section 344, certain light components (e.g., infraredlight) are reflected back into the first waveguide 350 and experienceTIR within that waveguide while other wavelength components are passedthrough the dichroic mirror into the second waveguide 351 and experienceTIR in that waveguide. Although not shown, it will be understood thatdichroic mirrors can also be positioned along the edges of thewaveguides 350, 351 to further determine whether particular lightcomponents within the respective waveguides exit the waveguides at anyparticular longitudinal edges, although this need not be the case in allembodiments.

Unlike the solar concentration section 294 of FIG. 20, however, each ofthe waveguides 350, 351 of the solar concentration section 344 is shownto include a respective longitudinal edge 352, 353, respectively, atwhich is positioned a respective folding prism 354, 355, respectively,as discussed above in relation to FIG. 15 (in alternate embodiments,reflectors can be employed in place of the folding prisms). As a resultof the folding prism 354, the light emanating from the first waveguide350, which can be infrared light, is directed to a first PV cell 356that is suited for receiving such light and that is positioned so as toextend parallel to the dichroic mirror 348 (that is, parallel to thewaveguides 350, 351) while light emanating from the second waveguide 351is directed to a second PV cell 357 that is suited for receiving suchlight (e.g., visible light). Thus, in the embodiment of FIG. 22, thesolar concentration section 344 achieves some of the same benefits ofeach of the solar concentration sections of FIG. 20 and FIG. 15, both interms of concentrating light and directing certain light components tosuitable PV cells, as well as arranging PV cells so as to be positionedin a desirable manner (and a manner in which the different PV cells arepositioned apart from one another). This embodiment can further allowfor the development of thin/small volume solar energy systems, andsystems with improved polarization performance.

Referring further to FIG. 23, an additional solar concentration section364 includes both the solar concentration section 4 of FIGS. 1-2 as wellas additional components that allow for the separation of differentlight components and direction of those respective light components todifferent PV cells. More particularly as shown, in the embodiment ofFIG. 23, a reflective output coupler 362 is positioned at an edge 28 ofthe waveguide 18 as shown and in turn directs the received light 360 toa dichroic reflector 366 that is located outside of the solarconcentration section 4. Due to the external dichroic reflector 366,certain light components (e.g., infrared light) are further reflected ina first direction toward a first PV cell 368 suitable for receiving thatlight while other light components are passed through the dichroicreflector and received by a second PV cell 370 suitable for receivingthose light components. This embodiment thus provides a simpleconcentrated design, where a concentration ratio can be reduced by afactor of z. To the extent that a common output angle from multimodewaveguide is desired, this can require additional reflection.

In view of the above, it should be noted that at least some embodimentsof the present invention achieve primary concentration of light bycollecting light over an entire lens array aperture and confining theenergy within a waveguide of constant thickness. The geometricconcentration is therefore the waveguide length divided by the waveguideslab thickness (or twice the thickness where there exists symmetriccoupling). Yet the aforementioned analysis of the concentration valueassumes no focusing in the orthogonal direction, that is, the directionperpendicular to the thickness of the waveguide (e.g., as measured alongthe normal axis 159 discussed above) and also perpendicular to thelength of the waveguide along which captured light generally proceedstoward one or more PV cells. Nevertheless, focusing in the orthogonaldirection can also be achieved in various manners and can result inadditional light concentration.

Referring to FIGS. 24A-24D for example, in at least some embodiments thePV cells need not occupy the entire widths of the edges of thewaveguides along which those PV cells are positioned. That is, the exitapertures (the portions of the edges of the waveguides along which PVcells are positioned) need not be coextensive with the edges of thewaveguides. For example, with respect to FIG. 24A, the slab waveguide 18of FIG. 1 having the first and second edges 28 and 30 need not beemployed in conjunction with PV cells that extend the full width of thewaveguide as do the PV cells 6 of FIG. 1. Rather, as shown in FIG. 24A,PV cells 372 can instead be employed that only extend approximatelyone-third of the width of the waveguide 18. Assuming that mirrors 374are positioned along the remaining portions of the edges 28, 30 that arenot covered by the PV cells 372, light within the waveguide 18 that isnot incident upon the PV cells continues to reflect back and forthwithin the waveguide 18 as represented by arrows 376 until such time asthe light enters into one of the PV cells 372. (A similar arrangementcan be employed to achieve separation of different light components fromone another). By reducing the size of the PV cells (and exit apertures)relative to the longitudinal waveguide edges in this manner, thegeometric concentration ratio is increased.

By comparison, FIG. 24 B also includes a waveguide 378 that has firstand second edges 379 and 380, respectively, and PV cells 382 and mirrors384 along each of the respective edges, where the PV cells occupy aboutone-third of the widths of each of those respective edges and themirrors along those edges occupy the remainders of the widths of thoserespective edges. In contrast to the embodiment of FIG. 24A, however,the edges 379, 380 of the waveguide 378 are not parallel to one anotherbut rather are tapered such that the overall waveguide has a trapezoidalshape as viewed normal to the waveguide (that is as viewed along theaxis 159 discussed above). By properly selecting the angles of suchtapered edges, reflection of the light (again as represented by arrows386) can be achieved that more rapidly results in arrival in the lightat the PV cells 382 than in the case of FIG. 24A. Although a trapezoidalarrangement is shown in FIG. 24B, it will be understood that othershapes are also possible including, for example, parallelogramarrangements or arrangements in which the edges of the waveguide arecurved. In each case, the edge configurations are selected so as toalter the reflection angles of the light being reflected off of themirrors along the edges of the waveguide so as to increase thelikelihood of reflections toward the PV cells and thus the likelihood ofcapture of that light by the PV cells.

FIG. 24C shows yet another waveguide 388. In this embodiment, a PV cell392 is only located along a first edge 390 of the waveguide while anopposite edge 391 of the waveguide is a mirror such that no light exitsthe waveguide at that edge. Thus, in such an embodiment, light isreflected not only by mirrored surfaces 394 existing along the firstedge 390 at which is located the PV cell 392 (which as in the cases ofFIGS. 24A-24B does not occupy the entire width of the edge) but also isreflected at the mirrored edge 391, as indicated by arrows 396. As forFIG. 24D, still an additional waveguide 398 is shown that also has thePV cell 392 and mirrored portions 394 along a first edge 397 but,instead of having a mirrored edge 391 as in FIG. 24C instead has an edge399 that is a Fresnel reflector or retroreflector (in the presentembodiment, the Fresnel reflector is a planar Fresnel reflector). Again,in the embodiments of FIGS. 24C and 24D, increased concentration oflight upon the PV cell 392 results. Further, from FIG. 24C it isapparent that a single PV cell can be used with symmetric coupling bymirroring one entire exit aperture of the slab waveguide, while asevidenced by FIG. 24D the use of other types of mirrors/prisms at oneedge of the waveguide can also be provided in some embodiments, forexample, where it is desired to achieve effectively the effect of acurved mirror on a planar surface.

Turning to FIGS. 25-28B, control or influence over the direction oflight proceeding within a waveguide such as the waveguides discussedabove can be achieved not only through the use of mirrors and lenses butalso by appropriate selection/configuration of the prism facets as well.In particular, every given prism facet can be configured to tend todirect/reflect light in a particular direction. Referring to FIG. 25, aschematic diagram illustrates one exemplary waveguide 400 within whichare positioned numerous prism facets 402. As shown, each of the prismfacets 402 is configured to direct/reflect light predominately in adirection indicated by a respective arrow emanating from that prismfacet. Further, as can be seen from FIG. 25, given appropriate selectionof such directional orientations of the prism facets 402, light from allof the prism facets can be directed generally towards a PV cell 404located at a given edge 406 of the waveguide 400.

Additionally, given the ability of prism facets to not only tilt raysfor the purpose of achieving TIR but also for the purpose oforientating/directing light towards a given region a waveguide (e.g.,toward a given edge or exit aperture of a waveguide, FIGS. 26A-26C showhow appropriate selection of the prism facets can be used to achievedirection of light towards any arbitrarily-located PV cell positionedalong an edge of a waveguide. More particularly, each of FIGS. 26A-26Cshow respective exemplary waveguides 410, 420, and 430, respectively, atwhich first, second and third PV cells 415, 425 and 435, respectively,are located at first, second and third positions along respective edgesof the respective waveguide. Although prism facets are not shown withparticularity in FIGS. 26A-26C, it will be noted that tangent curves417, 427 and 437 are shown instead. So long as the prism facets areconfigured to direct light in directions perpendicular to the respectivetangent curves 417, 427, and 437, in respective FIGS. 26A, 26B and 26C(and within the longitudinal plane of the waveguides), light will begenerally directed towards the respective PV cells 415, 425, 435 alongdirections generally indicated by respective arrows 419, 429 and 439,respectively. With respect to FIG. 26C specifically, it should befurther noted that two PV cells 435 are positioned along both oppositeedges of the waveguide 430, and it will be noted that there existssymmetry in the tangent curves 437 shown with respect to opposite halvesof the waveguide. Layout of the prism facets in the manner shown in FIG.26C can facilitate the manufacturing of numerous waveguides since theprism facet pattern is repetitive/cyclic (and thus the numerouswaveguides can be manufactured in any role type fashion).

Although the above description largely presumes that slab waveguides areemployed and that PV cells need to be positioned along edges of slabwaveguides, as illustrated in FIGS. 27-28B, this need not be the case insome embodiments. Indeed, the present invention is intended to encompassa variety of embodiments having a variety of different types and shapesof waveguides. For example, not only six-sided slab waveguides (or slabwaveguides with six edges) but also slab waveguides with more than sixsides/edges can be employed in some embodiments. Also, in someembodiments, the waveguides need not have sides/edges that are all flat,but instead can include one or more sides that are curved. Further,given appropriate prism facet configuration, light direction can becontrolled to such an extent that light can be effectively coupled to PVcells even though the PV cells merely occupy minor regions along one ormore of the non-edge surfaces (e.g., the surfaces 22, 24 of thewaveguide 18 of FIG. 1) of the waveguide.

Particularly as illustrated in FIG. 27, it is even possible to provide acircularly-shaped waveguide 440 having an outer cylindrical edge 442that is mirrored/reflective that effectively directs light to anoff-edge PV cell 444 by appropriately configuring prism facets 446 alongthat waveguide so as to direct light in the directions shown by arrowsemanating from those prism facets, that is, in directions toward thelocation of the PV cell. Due to the orientation of the prism facets 446,light is strongly directed toward the PV cell at the center of thewaveguide. Further due to the mirrored edge 442, light is also reflectedinward away from the outer cylindrical circumference as indicated by anarrow 448. As the light reflects back and forth between the varioussurfaces of the waveguide 440 it eventually proceeds to the location ofthe PV cells 444. The particular location of the PV cells 44 in terms ofwhether it is located on any particular one of the two non-edgedsurfaces (that is, the surfaces corresponding to the surfaces 22, 24 ofFIG. 1) is not critical due to the number of reflections that the lightwithin the waveguide 440 undergoes. In particular, there is no need forthe PV cell to extend into the waveguide in order for the PV cell tosatisfactorily receive light.

Given the ability to direct light within a given slab waveguide by wayof the prism facets (and also complementary mirrored surfaces), not onlycan a radial concentrator be realized having a single PV cell located atthe center of the disk, but also in some embodiments the disk can bereplaced with hexagonal sections to achieve higher fill factors betweenconcentrator elements. As shown in FIGS. 28A-28B, a plurality ofhexagonal slab waveguide portions 450 in particular can be assembled toform an overall waveguide assembly 452, where each of the waveguideportions 450 has a single associated PV cell 454 at its center towardwhich all light within that waveguide portion tends to be directed dueto the orientation of the prism facets. Exemplary orientation of prismfacets within a section of an exemplary hexagonal waveguide portion 450is shown in FIG. 28A (particularly in a section of one such waveguideportion), with the particular configured orientations of the prismfacets 456 being indicated by arrows emanating from those prism facets.It can be further noted that, in the rotationally-symmetric embodimentsof FIGS. 27-28B, the design of the coupling light extractor (e.g., interms of prism facet orientation) remains the same when rotated about acentral axis.

Because directionality of light flow within waveguides can be achievedat least in part by appropriate configuration of the prism facets, lightcan be further directed/coupled to PV cells with fewer passes along theslab waveguide and therefore achieve even greater efficiency. In atleast some embodiments of the present invention, it is envisioned thatthe use of prism facets to achieve directionality and greaterconcentration can be combined with the use of any one or more of theother above-described techniques (e.g., those involving lenses, mirrors,reflectors, light component separation, etc.) to achieve desireddirection of light within a slab waveguide toward PV cells and desiredconcentration of that light. That is, the above-described methodsinvolving light control using prism facets are independent of, but alsocombinable with, the other light-concentrating/extracting designs alsodescribed above.

In view of the above description, it should be apparent that the presentinvention is intended to encompass numerous embodiments having a varietyof different features, and the present invention encompasses numerousvariations on the particular embodiments discussed above as well. In atleast some additional embodiments of the present invention, a solarenergy system can employ one or more of the features shown above inrelation to one of the above-described systems with other features shownabove in relation to other(s) of the above-described systems. Also, oneor more of the features can be modified in many different manners. Forexample, in some alternate embodiments, it is possible to arrange prismfacets (or other injection features) along a surface of a waveguide thatis adjacent to a lens array rather than along the opposite side of thewaveguide. As already noted, a variety of different types of injectionfeatures can be implemented depending upon the application andembodiment.

From the above description, it should be apparent that, in at least someembodiments, the present invention involves new types of solarconcentrators that allow for efficient and inexpensive conversion ofsunlight to electric power. In at least some such solar concentrators,the concentrators collect sunlight from a large upward facing surfacehaving prism facets/injection features and channel the rays via totalinternal reflection (TIR) within an internal (slab waveguide) region,where they are directed towards the edges of the structure. One or morePV cells are placed at locations where light is allowed to leak forcollection and energy conversion. As described above, this can be at oneor more ends of the slab region, where the slab terminates and light canbe efficiently extracted. Yet in alternate embodiments, PV cells can beplaced periodically along the length of the slab waveguide by providinga structure/device that allows for guiding of the light out of the slabwaveguide and into the PV cells. In some such embodiments, this involvescreation of a sharply curved region of the slab waveguide proximate tothe PV cell. One or more simple bends in the slab waveguide/core willbreak the TIR conditions and can thus simply allow for the extraction oflight at several points along a concentrator.

Solar PV systems typically are placed in the outside environment towork, and are in general subject to degradation due to prolongedexposure to weather. In concentrated PV systems, the opticalconcentrator is exposed to weather, while the PV cell is typicallybetter protected. Recognizing that the PV cell is often the largestsingle cost element in the system, it is desirable to design a system sothat a functional PV cell and associated electronics can be ‘recycled’if the optical concentrator is damaged.

In this regard, in at least some of the embodiments of the presentinvention, the concentrator can be made as a continuous sheet which iscut to the desired length, then attached to a linear PV cell. The natureof a slab waveguide permits the guided light to be efficiently strippedfrom the guided mode and directed into the PV cell in several ways, forexample: (1) by cutting the end surface at an angle, (2) by removing thecladding or providing an index-matching layer between the waveguide andthe PV cell, or (3) by introducing a sharp physical curvature or bendinto the waveguide, so that the light is incident at less than thecritical angle for total internal reflection. These features can bepre-formed into the waveguide sheet, but they can also be incorporatedinto the mounting for the PV cell, so as to be readily implemented inrelation to (for action upon) any region of a waveguide to which theyare attached.

Therefore, it is possible to design a linear photovoltaic cell with amounting that clamps onto the waveguiding concentrator sheet, creatingthe feature that will strip the guided light and direct it into thephotovoltaic cell without the need for accurate alignment. Assuming sucha design, it is possible to have a modular concentrated photovoltaicsystem where one or more photovoltaic cells (and associated electricalconnections) can be attached to and/or removed from an opticalconcentrator in the field, both for the initial installation, andsubsequently for maintenance (e.g., if the optical concentrator needs tobe replaced due to environmental damage). Further, recognizing that theoverall collection efficiency of a waveguide-based concentrator dependson the distance to the PV cell, it is possible to install a large-areaconcentrator with a single PV cell and subsequently upgrade the overallpower output performance of the system by subsequently adding more PVcells.

A slab waveguide typically is a multiple optical mode structure whichcan guide light without loss as it propagates through the slab. A slabwaveguide typically consists of a high index core surrounded by a lowerindex cladding on the top and/or bottom. Converting light from normalincidence on the face of the slab into light which is propagating withinthe slab requires some kind of structure for deflecting the light, whichwill not then act to eject (or allow excessive escaping of) lightalready trapped within the slab. One way to achieve proper guiding is toprovide a localized coupling region with an index comparable to thecore. As described, in at least some embodiments, this can involve usinga colloidal suspension of high-index, sub-wavelength-sized, particleswithin a lower index liquid. Bright incident light causes opticaltrapping, increasing the density of the high index particles and soincreasing the overall refractive index where the incoming lightaccumulates the particles yielding an increase in the average index ofrefraction. A localized increase in the refractive index allows lightthat scatters from the suspended particles, or reflects from a nearbyoptical structure (which is otherwise not interacting with the guidedlight within the slab), to be trapped within the slab region and guidedto the PV cell.

At least some embodiments of the above-described solar energysystems/solar concentrators are suited for the roll-to-roll processingmethod of manufacture. A roll process produces the lenslets by embossingthem onto a layer of low index plastic which covers the higher indexslab region. The back surface can be made using a similar process, forthe actively aligned version, or using a sandwich of materials, such asa perforated mesh separating a liquid-filled layer from a patterned rearsurface. In all cases, the multiple layers of the concentrator can belaid onto one continuous substrate creating a long, flexible product ata very low cost. Alternately the concentrator can be formed onto rigidpanels using a more conventional, if more expensive, manufacturingprocess.

Thus, in at least some embodiments, the present invention involves anoverall slab waveguide concentrator geometry using focusing lenses andlocalized injection features, where either the localized injectionfeatures are permanent or alternatively the injection features arereactive (formed in response to incident light), where multiple specificmaterials and structures can be used for formation of the injectionfeatures. The slab waveguide format is extremely compact in comparisonto many conventional active or passive concentrator optics. Sincematerial costs are a significant part of the overall system cost, thisentails a potential cost savings.

Also, as noted, in the embodiments employing reactive solarconcentrators, the reactive nature of the concentrators eliminates theneed for the active tracking usually associated with solarconcentration. Indeed, such embodiments are distinctive in that noabsorption is required. The reacting material can potentially reactlosslessly, as for example through a change in index. Even if thereacting material does require some absorption, the light which isguided within the slab does not (on average) encounter the reactingmaterial again, and so would experience only a single loss point. Thegeometries of at least some of these embodiments are attractive in thatvery high input to output area ratios can be achieved. Although someembodiments will incorporate a lens array and therefore only work withspecular light, there is the potential for significantly less loss byavoiding the absorption and remission of photons. The overall geometrymaintains the advantage of a high collection area and incorporates areactive, index-changing material to avoid active tracking.

The highest conversion efficiency photovoltaic cells requireconcentration of incident sunlight to work with maximum efficiency(typically 100-1000× concentration). However, concentrator optics arefundamentally incapable of efficiently collecting diffuse sunlight ontoa small area photovoltaic cell. Therefore, the efficiency of a highlyconcentrated photovoltaic system drops to nearly zero on cloudy days,whereas non-concentrated photovoltaic systems (such as an amorphoussilicon solar panel) substantially maintain their performance. Giventhese considerations, and further in view of the fact that many solarinstallations (such as for residential and commercial rooftops) involvelimited areas upon which the solar collectors can be implemented, atleast some embodiments of the present invention are intended facilitateachieving the benefits associated with both concentrated PV systems aswell as non-concentrated photovoltaic systems by both collecting directsunlight into a concentrated high-efficiency photovoltaic cell, and also(possibly simultaneously) directing diffuse sunlight into a lessefficient photovoltaic cell.

In this regard, at least some embodiments of the present inventioninvolve extracting and concentrating the direct sunlight to the edge ofthe illuminated area for reception by one or more PV cell(s), whileallowing diffuse light to pass through the waveguide for collection byone or more other PV cell(s). Referring again to FIG. 1, light whichenters the lens array 8 normally is focused onto the replicated prismfacets 26 and coupled into the slab waveguide 18. In some embodiments(e.g., that of FIG. 10), light which enters the lens array 8 at anyother angle is focused by the lenslets onto a transparent region of therear surface of the waveguide, missing the prism facets 26, and istransmitted through the rear surface of the waveguide 24 substantiallywithout attenuation. Therefore, an area-efficient hybrid photovoltaicsystem can be made by placing a conventional solar panel directlybeneath the micro-optic slab concentrator. On cloudless days, most ofthe energy would be generated by the efficient photovoltaic cell via theconcentrator. By comparison, on cloudy days, a smaller total amount ofenergy, bypassing the slab concentrator, would be generated mostly bythe photovoltaic panel.

Each of the above-described embodiments of solar energy systems/solarconcentrators are potentially manufacturable at extremely low cost, ascompared with the cost of manufacturing conventional PV cell materialfrom amorphous or crystalline Silicon. Due to the compliance withroll-to-roll processing, it is likely that this concentrator design willexist as flexible sheets several meters in length. They could be fittedonto roofs or act as tents to provide local power generation for homesor temporary installations. Smaller units can be applicable for thepowering of laptop computers or other small electronics. At least someof the above-described embodiments can be made from flexible materials,as each local region is automatically aligned with the incident light.This supports low cost deployment and unconventional uses: for exampleas tent material or ground cover over non-flat terrain. Although theabove description describes physical orientations of various componentsof solar energy systems relative to one another (e.g., where onecomponent is “above” or “below” another component), these terms are onlyprovided to facilitate description of these embodiments but are notintended to limit the present invention to embodiments satisfying theseparticular characteristics.

It is specifically intended that the present invention not be limited tothe embodiments and illustrations contained herein, but include modifiedforms of those embodiments including portions of the embodiments andcombinations of elements of different embodiments as come within thescope of the following claims.

1. A system for capturing solar energy, the system comprising: a firstlens array having a plurality of lenses; a second lens array, whereinthe second lens array has a mirrored surface and wherein each of thelenses of the second lens array is aligned with a respective one of thelenses of the first lens array such that light received by the systemfor capturing solar energy is partially focused upon passing through thefirst lens array and further focused upon reflection from the secondlens array to form a focal spot on a plane that lies between the firstand the second lens arrays.
 2. The system of claim 1, further comprisingan optical waveguide layer located between the first lens array and thesecond lens array, wherein the optical waveguide layer includes an arrayof injection features wherein each of the injection features ispositioned to receive reflected light from at least one of the lenses ofthe second lens array and to direct the reflected light to the opticalwaveguide layer.
 3. The system of claim 2, wherein each injectionfeature is triangular in cross section, with at least one reflectivesurface that directs the reflected light in the optical waveguide layer.4. The system of claim 2, wherein the optical waveguide layer isseparated from the first lens array by a first cladding layer and isseparated from the second lens array by a second cladding layer.
 5. Thesystem of claim 2, wherein each of the injection features is located ator near a focal spot of a lens of the second lens array, and whereineach injection feature is oriented so that at least some of thereflected light is coupled into the optical waveguide layer.
 6. Thesystem of claim 2, wherein at least some of the light directed to theoptical waveguide layer is guided within the optical waveguide layer bytotal internal reflection.
 7. The system of claim 2, wherein the opticalwaveguide layer is laterally shiftable relative to the first or thesecond lens arrays so that incident light arriving at the system forcapturing solar energy is received by the injection features uponreflection from the second lens array even though an angle of incidenceof the incident light arriving at the system for capturing solar energyvaries with time.
 8. The system of claim 7, further comprising one ormore actuators and a controller that adjusts a position of the opticalwaveguide layer relative to the first lens array and the second lensarray to enable alignment of the injection features with the foci of thelight reflected from the second lens array.
 9. The system of claim 7,further comprising one or more sensors that detect the angle ofincidence of the incident light and provide a signal to the controller.10. A method of manufacturing a solar energy collection system,comprising: providing a first lens array; providing a second lens arraywith a mirrored coating; molding a prism array from anultra-violet-curable polymer film; positioning the prism array betweenthe first and second lens arrays.
 11. The method of claim 10, furthercomprising: providing one or more cladding films having lower refractiveindex than the first lens array or the second lens array; and placingthe one or more cladding films between the prism array and the firstlens array or the second lens array to form a light-guide.
 12. Themethod of claim 10, further comprising: depositing a reflective coatingon facets of the prism array.
 13. The method of claim 10, furthercomprising: crosslinking specific portions of the ultraviolet-curablepolymer film by exposing the first or the second lens arrays and theprism array to ultraviolet light and subsequently rinsing the first orthe second lens arrays and the prism array in a solvent to removeuncured polymer material.
 14. The method of claim 13, wherein theultraviolet light is directed through the first lens array or the secondlens array.